Photos shared on social media show a large knife lying on the pavement on Parliament Street next to a smaller knife, and a policeman in forensic gear taking photographs of a bag abandoned next to them.

The suspect was reportedly wrestled to the ground on a traffic island at the Parliament end square of Whitehall, close to the Foreign Office and the entrance to Downing Street.

He was seen pinned up against the wall of the HMRC offices before being taken away in a police vehicle.

Eyewitnesses told the Evening Standard a man had been carrying “a rucksack of knives.”

Luke William told the newspaper he was driving past as police flooded the area. “There was a man being held against the wall by armed police. On the floor was a backpack with knives falling out of it.”

Photos showed a police cordon surrounding the bag, which had been discarded on a road traffic island.